The present invention pertains to processes for the preparation of highly branched polymers and aromatic polyesters. More particularly, the present invention pertains to processes for the preparation of multiply-branched aromatic polyesters.
Highly branched, non-crosslinked polymers have been prepared by "multiple generation" and "single generation" procedures. The multiple generation procedures are exemplified by Tomalia, D. A., et al, Angewandte Chemie, International Edition in English, 29, 138-175 (1990) and U.S. Pat. No. 5,041,516 to Frechet, J. M. J. et al, which describe the preparation of highly branched, non-crosslinked polyamidoamines and polybenzyl ethers, respectively. Tomalia et al identified the polymers produced as "starburst polymers" or "starburst dendrimers". Both publications describe preparations in which the macromolecules were prepared by repeatedly reacting, isolating and purifying a product through a series of growth steps. The product of each growth step is called a "generation". These procedures are highly laborious, but the product produced is highly uniform. Newkome et al, Journal of the American Chemical Society, Vol. 112, 8458, (1990) describes a similar step and repeat process used to build up various macromolecules described as tree-like and identified as "arborols".
Single generation procedures are much less laborious than multiple generation procedures. The single generation procedures are exemplified by Flory, P. J., Journal of the American Chemical Society, 74, p. 2718 (1952), which presents a theoretical analysis of the formation of highly branched, soluble polymers from monomers having the structure AB.sub.x, in which A and B are the reactive groups, by condensation polymerization, with random branching and without cross-linking. Kim, Y. H. et al, Journal of the American Chemical Society, Vol. 112, p. 4592 (1990) and U.S. Pat. No. 4,857,630 to Y. H. Kim, describe this kind of "single generation" approach in the preparation of hyperbranched polyphenylenes. U.S. Pat. No. 3,669,939 to Baker, A. S. et al teaches highly branched, non-crosslinked, aliphatic polyesters, prepared by a "single generation" melt condensation polymerization of monomers having a single carboxylic acid functionality and multiple alcohol functionalities. Hawker, C. J., Lee, R. and Frechet, M. J. M., Journal of the American Chemical Society, Vol. 113, No. 12, (1991) pp 4583-4588, teaches a single generation procedure for the preparation of all aromatic, highly-branched, non-cross-linked polyesters. In this procedure, 3,5-bis(trimethylsiloxy)benzoyl chloride is melt polymerized by the Kricheldorf method, described in H. R. Kricheldorf et al, Makromol. Chem. 184 , 475 (1983), driving off trimethylsilylchloride. The product can be subjected to hydrolysis to provide phenolic terminated highly branched polyesters. This procedure has the shortcomings of requiring expensive, water-sensitive reactants and difficult monomer preparation steps.
Linear and some slightly branched aromatic polyesters are often prepared via the "acetolysis" reaction. The use of this kind of reaction to produce a highly-branched non-crosslinked aromatic polyester has not been reported and what has been reported in the literature would lead one skilled in the art to expect that such chemistry would not perform well for the synthesis of highly branched polymers. Kricheldorf, H. R. et al in Makromol. Chem. 184, 475 (1983) and R. Gilky et al, Journal of Applied Polymer Science, 2, 198 (1959) indicated that in the preparation of poly(hydroxybenzoic acid) the condensation reaction using the acetate is accompanied by a decarboxylation side reaction. Such a decarboxylation reaction would inhibit formation of highly-branched polymer by causing large defects or low molecular weight or both. In addition Kricheldorf, H. R. et al in Polymer 23, 1821 (1982) indicated that several attempts to use 3,5-diacetoxybenzoic acid as a branching component in a co-condensation polymerization with m-hydroxybenzoic acid resulted in little if any branching. Kricheldorf states on page 1827 that ". . . the second acetyl group of (3,5-diacetoxybenzoic acid) after incorporation of the trifunctional monomer into the linear chain is not reactive enough to initiate the branching step."